
The ABO Blood Groups

Genotype	Antigen	Phenotype


I^AI^A	A	A
I^AI^O	A	A

I^BI^B	B	B
I^BI^O	B	B

I^AI^B	A, B	AB

I^OI^O	Neither	O

The human ABO blood group is affected by multiple alleles.

An individual is A, B, AB, or O phenotype as a result of dominance of the I^A and I^B alleles to the I^O allele and codominance of the I^A and I^B alleles to each other.